//*****************************************************************************
// METHOD: intersectRay()
//
// Service method for intersecting a ray with the elevation surface to
// arrive at a ground point. The ray is expected to originate ABOVE the
// surface and pointing down.
//
// NOTE: the gpt argument is expected to be initialized with the desired
// datum, including ellipsoid, for the proper intersection point to be
// computed.
//
// LIMITATION: This release supports only single valued solutions, i.e., it
// is possible a ray passing through one side of a mountain and out the other
// will return an intersection with the far side. Eventually, a more robust
// algorithm will be employed.
//
//*****************************************************************************
bool ossimElevSource::intersectRay(const ossimEcefRay& ray, ossimGpt& gpt, double defaultElevValue)
{
if (traceExec()) ossimNotify(ossimNotifyLevel_DEBUG) << "DEBUG ossimElevSource::intersectRay: entering..." << std::endl;
static const double CONVERGENCE_THRESHOLD = 0.001; // meters
static const int MAX_NUM_ITERATIONS = 50;
double h_ellips; // height above ellipsoid
bool intersected;
ossimEcefPoint prev_intersect_pt (ray.origin());
ossimEcefPoint new_intersect_pt;
double distance;
bool done = false;
int iteration_count = 0;
if(ray.hasNans())
{
gpt.makeNan();
return false;
}
//***
// Set the initial guess for horizontal intersect position as the ray's
// origin, and establish the datum and ellipsoid:
//***
const ossimDatum* datum = gpt.datum();
const ossimEllipsoid* ellipsoid = datum->ellipsoid();
// double lat, lon, h;
// ellipsoid->XYZToLatLonHeight(ray.origin().x(),
// ray.origin().y(),
// ray.origin().z(),
// lat, lon, h);
// ossimGpt nadirGpt(lat, lon, h);
// std::cout << "nadir pt = " << nadirGpt << std::endl;
gpt = ossimGpt(prev_intersect_pt, datum);
//
// Loop to iterate on ray intersection with variable elevation surface:
//
do
{
//
// Intersect ray with ellipsoid inflated by h_ellips:
//
h_ellips = getHeightAboveEllipsoid(gpt);
if ( ossim::isnan(h_ellips) ) h_ellips = defaultElevValue;
intersected = ellipsoid->nearestIntersection(ray,
h_ellips,
new_intersect_pt);
if (!intersected)
{
//
// No intersection (looking over the horizon), so set ground point
// to NaNs:
//
gpt.makeNan();
done = true;
}
else
{
//
// Assign the ground point to the latest iteration's intersection
// point:
//
gpt = ossimGpt(new_intersect_pt, datum);
//
// Determine if convergence achieved:
//
distance = (new_intersect_pt - prev_intersect_pt).magnitude();
if (distance < CONVERGENCE_THRESHOLD)
done = true;
else
{
prev_intersect_pt = new_intersect_pt;
}
}
iteration_count++;
} while ((!done) && (iteration_count < MAX_NUM_ITERATIONS));
if (iteration_count == MAX_NUM_ITERATIONS)
{
if(traceDebug())
{
ossimNotify(ossimNotifyLevel_WARN) << "WARNING ossimElevSource::intersectRay: Max number of iterations reached solving for ground "
<< "point. Result is probably inaccurate." << std::endl;
}
}
if (traceExec()) ossimNotify(ossimNotifyLevel_DEBUG) << "DEBUG ossimElevSource::intersectRay: returning..." << std::endl;
return intersected;
}
